1 Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, United Kingdom, 2 Faculty of Medical Sciences, University College London, London, United Kingdom,3 Faculty of Public Health and Policy, London School of Hygiene & Tropical Medicine, London, United Kingdom, 4 Humanitarian Public Health Technical Unit, Save the Children UK, London, United Kingdom, 5 Transfusion Microbiology, National Health Service Blood and Transplant, London, United Kingdom, 6 NHSBT/PHE Blood Borne Virus Unit, Serology Development Unit, Public Health England, London, United Kingdom, 7 Centre of Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom, 8 Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom, 9 Department of Infection and Tropical Medicine, University Hospitals of Leicester NHS Trust, Leicester, United Kingdom

† Deceased.

Abstract

Background

Healthcare and other front-line workers are at particular risk of infection with Ebola virus (EBOV). Despite the large-scale deployment of international responders, few cases of Ebola virus disease have been diagnosed in this group. Since asymptomatic or pauci-symp- tomatic infection has been described, it is plausible that infections have occurred in health- care workers but have escaped being diagnosed. We aimed to assess the prevalence of asymptomatic or pauci-symptomatic infection, and of exposure events, among returned responders to the West African Ebola epidemic 2014–2016.

Methods and findings

We used snowball sampling to identify responders who had returned to the UK or Ireland, and used an online consent and questionnaire to determine their exposure to EBOV and their experience of illness. Oral fluid collection devices were sent and returned by post, and samples were tested using an EBOV IgG capture assay that detects IgG to Ebola glycopro- tein. Blood was collected from returnees with reactive samples for further testing. Unex- posed UK controls were also recruited.

In all, 300 individuals consented, of whom 268 (89.3%) returned an oral fluid sample (OFS). The majority had worked in Sierra Leone in clinical, laboratory, research, and other roles. Fifty-three UK controls consented and provided samples using the same method.

Of the returnees, 47 (17.5%) reported that they had had a possible EBOV exposure. Based on their free-text descriptions, using a published risk assessment method, we classi- fied 43 (16%) as having had incidents with risk of Ebola transmission, including five interme- diate-risk and one high-risk exposure. Of the returnees, 57 (21%) reported a febrile or diarrhoeal illness in West Africa or within 1 mo of return, of whom 40 (70%) were not tested at the time for EBOV infection.

Of the 268 OFSs, 266 were unreactive. Two returnees, who did not experience an illness in West Africa or on return, had OFSs that were reactive on the EBOV IgG capture assay, with similar results on plasma. One individual had no further positive test results; the other had a positive result on a double-antigen bridging assay but not on a competitive assay or on an indirect EBOV IgG ELISA. All 53 controls had non-reactive OFSs. While the partici- pants were not a random sample of returnees, the number participating was high.

Conclusions

This is the first study, to our knowledge, of the prevalence of EBOV infection in international responders. More than 99% had clear negative results. Sera from two individuals had dis- cordant results on the different assays; both were negative on the competitive assay, sug- gesting that prior infection was unlikely. The finding that a significant proportion experienced “near miss” exposure events, and that most of those who experienced symptoms did not get tested for EBOV at the time, suggests a need to review and standardise protocols for the management of possible exposure to EBOV, and for the management of illness, across organisations that deploy staff to outbreaks.